Method of manufacturing pipe member

ABSTRACT

A method of manufacturing a pipe member includes arranging a pre-pipe member between first and second dies, moving one of the first and second dies to be closer to another one and holding the pre-pipe member with first and second recess portions, by the moving of the one of the first and second dies, and pressing an outer peripheral surface of the pre-pipe member with first and second inner surfaces in a closed state of the dies. By the pressing of the outer peripheral surface of the pre-pipe member, reducing a diameter of a portion of the pre-pipe member and forming a reduction portion having a polygonal shape so that the reduction portion has a same number of outer surfaces as a total number of the first inner surfaces and the second inner surfaces.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2015-199126 filed on Oct. 7, 2015. The entire contents of the priority application are incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a method of manufacturing a pipe member.

BACKGROUND OF THE INVENTION

A pipe may have a tapered portion in a middle of a pipe path or may have a portion having a hexagonal outer peripheral shape. Specifically, swaging processing is carried out to reduce a diameter of a part of a hollow exhaust pipe (a pipe member). Thus, a tapered portion where an outer diameter of the pipe is gradually reduced is formed.

SUMMARY OF THE INVENTION

However, if the pipe path is to be changed or the outer peripheral shape of the pipe is to be changed with the swaging process, the outer peripheral surface is continuously hit while changing a phase of the pipe member, and an expensive, specialized device is required. Pipe members are processed one by one by changing an angle thereof with respect to a hitting device. The pipe member may be bent during the swaging process depending on a required processing accuracy. To prevent this from occurring, a core bar is usually inserted into the pipe member. However, it might not be possible to insert the core bar into the pipe member due to the shape of the pipe.

The present technology has been made in view of the aforementioned circumstances. An objective of the present technology is to provide a method of manufacturing a pipe member easily and with reduced cost.

To solve the above problem, according to the present technology, a method of manufacturing a pipe member includes arranging a first die including a first recess portion that has first inner surfaces and a second die including a second recess portion that has second inner surfaces such that the first recess portion is opposite the second recess portion, arranging a pre-pipe member between the first die and the second die, the pre-pipe member having an elongated tubular shape, moving one of the first die and the second die to be closer to another one of the first die and the second die and holding the pre-pipe member with the first recess portion and the second recess portion, by the moving of the one of the first die and the second die, pressing an outer peripheral surface of the pre-pipe member with the first inner surfaces and the second inner surfaces in a closed state where the first die and the second die are closed, by the pressing of the outer peripheral surface of the pre-pipe member, reducing a diameter of a portion of the pre-pipe member and forming a reduction portion having a polygonal shape so that the reduction portion has a same number of outer surfaces as a total number of the first inner surfaces and the second inner surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a camshaft including a shaft (a pipe member) manufactured with a method according to the present technology.

FIG. 2 is a perspective view of a pre-pipe member during a reduction process.

FIG. 3 is a cross-sectional view of the pre-pipe member arranged between a first die and a second die during the reduction process.

FIG. 4 is a cross-sectional view of the pre-pipe member arranged between a first recess portion and a second recess portion such that an outer peripheral surface of the pre-pipe member is in contact with a part of the first inner surfaces and a part of the second inner surfaces, and FIG. 4 is a cross-sectional view taken along line V-V in FIG. 2.

FIG. 5 is a cross-sectional view of the pre-pipe member between the first die and the second die that are closed.

FIG. 6 is a perspective view of a shaft including a hexagonal portion.

FIG. 7 is a cross-sectional view of a shaft having a tapered end portion and taken along VI-VI line in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present technology will be described with reference to FIGS. 1 to 7. A holding member 70 is not described in FIGS. 3 to 5. A camshaft 340 described in FIG. 1 is one of components included in an engine and includes one shaft (a pipe member) 30. The shaft 30 collectively includes multiple cams 40 (41-48) that are configured to open or close intake and exhaust valves included in the engine. The cams (41-48) are mounted on the shaft 30 to be rotated integrally therewith. The shaft 30 includes a hexagonal portion 55 having a regular hexagonal cross-sectional shape between the adjacent cams 42 and 43 that are on a left side in the drawing. When the cams 40 are mounted on the shaft 30, a position of each cam 40 is adjusted with the hexagonal portion 55 being held between distal ends of a tool such as a wrench (not illustrated). Specifically, opposite surfaces of the hexagonal portion 55 having a hexagonal cross-sectional shape are in contact with the distal ends of the tool. The hexagonal portion 55 is formed by reducing a diameter of a pre-pipe member 50 having an elongated tubular shape (cylindrical shape) and the diameter of the pre-pipe member 50 is reduced in one end portion thereof to have the hexagonal portion 55 having a hexagonal cross-sectional shape (see FIG. 6).

A method of manufacturing the shaft 30 having the hexagonal portion 55 illustrated in FIG. 6 will be described. First, an elongated cylindrical tubular pre-pipe member 50 is manufactured. STKM13C is used as a material of the pre-pipe member 50 and STKM is a general material for a pipe member. The pre-pipe member 50 is manufactured with ATKM13C to have an outer diameter of 25 mm and a thickness of 3.5 mm. Then, the pre-pipe member 50 is subjected to a reduction process, and a desired portion of the pre-pipe member except for the end portions is subjected to the reduction process so that the diameter thereof is reduced to have a regular hexagonal cross-sectional shape.

As illustrated in FIGS. 2 to 5, a press molding device is used in the reduction process and the press molding device includes a first die 10 and a second die 20. The first die 10 is on an upper side and the second die 20 is on a lower side. The first die 10 includes a first recess portion 10A on a surface 11 opposite the second die 20 and the first recess portion 10A has multiple surfaces. The multiple surfaces are three surfaces including first side inner surfaces 101, 103 that are opposite each other and a first recessed inner surface 102 that is between the first side inner surfaces 101, 103. The first side inner surfaces 101, 103 and the first recessed inner surface 102 correspond with three surfaces of the hexagonal portion 55 that has a regular hexagonal cross-sectional shape and is to be formed in a portion of the pre-pipe member 50.

The second die 20 includes a second recess portion 20A on a surface 21 opposite the first die 10 and the second recess portion 20A has multiple surfaces. The multiple surfaces are three surfaces including second side inner surfaces 204, 206 and a second recessed inner surface 205 that is between the second side inner surfaces 204, 206. The second side inner surfaces 204, 206 and the second recessed inner surface 205 correspond with another three surfaces of the hexagonal portion 55 that has a regular hexagonal shape and is to be formed in a portion of the pre-pipe member 50. Hereinafter, the general reference of the first inner surfaces including the first side inner surfaces 101, 103 and the first recessed inner surface 102 will be referred to as the first inner surfaces 100 and the general reference of the second inner surfaces including the second side inner surfaces 204, 206 and the second recessed inner surface 205 will be referred to as the second inner surfaces 200.

As illustrated in FIG. 5, the first die 10 and the second die 20 are closed so that the regular hexagonal shape is defined by the first inner surfaces 100 and the second inner surfaces 200. In the closed state, the first inner surfaces 100 and the second inner surfaces 200 are opposite each other, respectively, with a distance of 22 mm between the opposite surfaces 100 and 200. Specifically, as illustrated in FIG. 5, the first inner surface 101 is opposite the second inner surface 204, the first inner surface 102 is opposite the second inner surface 205, and the first inner surface 103 is opposite the second inner surface 206. The distance Y between the respective first inner surfaces and the respective second inner surfaces is 22 mm.

A ratio of the distance between the opposite surfaces to an outer diameter X of the pre-pipe member 50 is approximately 0.88. The opposite surfaces are the respective first inner surfaces 100 and the respective second inner surfaces 200 in the closed state of the first die 10 and the second die 20. The distance Y between the opposite surfaces is preferably from 0.77X to 0.95X with respect to the outer diameter X of the pre-pipe member 50. The opposite surfaces are the respective first inner surfaces 100 and the respective second inner surfaces 200 in the closed state of the first die 10 and the second die 20. If the distance Y between the opposing surfaces is less than 0.77X, a part of the pre-pipe member 50 may go outside the molding recess portion. If the distance Y between the opposing surfaces is greater than 0.95X, a desired hexagonal shape may not be formed.

As illustrated in FIG. 3, the pre-pipe member 50 is arranged between the first inner surfaces 100 of the first recess portion 10A of the first die 10 and the second inner surfaces 200 of the second recess portion 20A of the second die 20 and then, the first die 10 and the second die 20 are moved closer to each other and closed. The first die 10 and the second die 20 are closed while holding the pre-pipe member 50 between the first side inner surfaces 101, 103 and the second side inner surfaces 204, 206, as illustrated in FIG. 4. According to the closing of the dies 10, 20, the pre-pipe member 50 is pressed by the first side inner surfaces 101, 103 and the second side inner surfaces 204, 206 so that the outer peripheral surface of the pre-pipe member 50 is pressed toward an axial center thereof. The first die 10 and the second 20 are further moved closer to each other, and the first recessed inner surface 102 and the second recessed inner surface 205 are brought in contact with the pre-pipe member 50 and the pre-pipe member 50 is pressed by the first side inner surfaces 101, 103, the first recessed inner surface 102, the second side inner surfaces 204, 206, and the second recessed inner surface 205. A load applied to the pre-pipe member 50 in the closing of the first and second dies 10, 20 is approximately 100 kN.

The distance Y between the opposing surfaces of the first recess portion 10A and the second recess portion 20A in the closed state of the dies 10 and 20 is 22 mm and the outer diameter X of the pre-pipe member 50 is 25 mm. Thus, the outer diameter X of the pre-pipe member 50 is greater than the distance Y between the opposing surfaces. Therefore, as the first die 10 and the second die 20 are moved closer to each other to be closed, the first side inner surfaces 101, 103 and the second side inner surfaces 204, 206 are first in contact with the pre-pipe member 50 and press an outer peripheral surface 50M of the pre-pipe member 50 so that a force Y1 is applied to the pre-pipe member 50 and contact portions of the outer peripheral surface 50M start to be plastically deformed.

When the first die 10 and the second die 20 are moved closer to each other to be completely closed and in a closed state, the pre-pipe member 50 is further pressed and further plastically deformed. Accordingly, the first inner surface 102 that is on an upper side and the second inner surface 205 that is on a lower side are in contact with the outer peripheral surface 50M of the pre-pipe member 50 and contact portions of the pre-pipe member 50 in contact with the first inner surface 102 and the second inner surface 205 are also plastically deformed.

Thus, when the first die 10 and the second die 20 are closed, the first die 10 and the second die 20 apply pressure to the outer peripheral surface 50M of the pre-pipe member 50 via the first inner surfaces 100 and the second inner surfaces 200. In a final closed state of the first die 10 and the second die 20, a reduction portion of a polygonal cross-sectional shape is formed on the outer peripheral surface of the pre-pipe member 50. The polygonal shape is a hexagonal shape defined by the three first inner surfaces 100 (101, 102, 103) and the three second inner surfaces 200 (204, 205, 206). Accordingly, the shaft 30 includes the hexagonal portion 55 on a part of the peripheral surface thereof and the hexagonal portion 55 has a regular hexagonal cross-sectional shape.

As illustrated in FIG. 2, in the reduction process, the pre-pipe member 50 is inserted in a holding hole 70A of a holding member 70. Specifically, a portion of the pre-pipe member 50 near the portion that is to be pressed with the first die 10 and the second die 20 is held by the holding member 70 from an outer periphery of the pre-pipe member 50. The holding member 70 has an elongated cylindrical tubular shape similar to the pre-pipe member 50 and has an inner diameter size that follows an outer diameter of the pre-pipe member 50. Thus, the outer periphery of the pre-pipe member 50 is held by the holding member 70. Therefore, the pre-pipe member 50 is less likely to be bent when a load is applied thereto from the first die 10 and the second die 20.

A hexagonal portion 255 is formed on a pre-pipe member having a tapered end portion 250T to manufacture a shaft 230 as illustrated in FIG. 7. In manufacturing such a shaft 230, the core bar cannot be inserted in the shaft 230 and therefore, it is effective to hold the portions of the pre-pipe member except for the portion to be the hexagonal portion 255 with the holding member 70 from the outer periphery.

Next, operations and advantageous effects of the present embodiments will be described.

According to the method of manufacturing the shaft 30, the first die 10 and the second die 20 are closed and press the pre-pipe member 50 from the outer periphery thereof so that a part of the outer peripheral surface is processed to have the polygonal shape on the outer peripheral surface 50M of the pre-pipe member 50 via one reduction process. Accordingly, time required for the manufacturing process of the shaft 30 is shortened. A polygonal portion is formed with the reduction process at a low cost compared to a method using an expensive device that is exclusively used in the swaging process.

According to the method of manufacturing the shaft 30, the first die 10 has three surfaces for forming three surfaces of a regular hexagonal shape of the hexagonal portion 55 and the second die 20 has three surfaces for forming another three surfaces of the regular hexagonal shape of the hexagonal portion 55. The opposing surfaces of the first inner surfaces 100 and the second inner surfaces 200 have the distance Y therebetween when the first die 10 and the second die 20 are closed, and the distance Y is from 0.77X to 0.95X where X is the outer diameter of the pre-pipe member 50. In the reduction process, when the first die 10 and the second die 20 are closed, pressure force is applied to the outer peripheral surface of the pre-pipe member 50 via the three surfaces of the first die 10 and the three surfaces of the second die 20. Therefore, the pressure force is easily applied to the outer peripheral surface 50M of the pre-pipe member 50 while holding the outer peripheral surface 50M and a reduction portion having a desired regular hexagonal cross-sectional shape is precisely formed with the reduction process.

According to the method of manufacturing the shaft 30, the hexagonal portion 55 (a polygonal reduction portion) is formed in a middle portion of the shaft 30 that is an axis of the camshaft 340. Therefore, the hexagonal portion 55 (polygonal reduction portion) is useful in adjusting the positions of the cams 40.

According to the method of manufacturing the shaft 30, the pre-pipe member 50 is held by the holding member 70 via the outer periphery thereof. Therefore, the pre-pipe member 50 is less likely to be deformed in executing the reduction process for the pre-pipe member 50. Even in executing the reduction process for the pre-pipe member 50 having the shape where the core bar cannot be inserted therein, the pre-pipe member 50 is held by the holding member 70 from the outer peripheral surface thereof, and the pre-pipe member 50 is less likely to be bent. 

1. A method of manufacturing a pipe member, the method comprising: arranging a first die including a first recess portion that has first inner surfaces and a second die including a second recess portion that has second inner surfaces, such that the first recess portion is opposite to the second recess portion; arranging a pre-pipe member between the first die and the second die, the pre-pipe member having an elongated tubular shape; and moving one of the first die and the second die to be closer to another one of the first die and the second die and holding the pre-pipe member with the first recess portion and the second recess portion, wherein the moving of the one of the first die and the second die comprises pressing an outer peripheral surface of the pre-pipe member with the first inner surfaces and the second inner surfaces in a closed state where the first die and the second die are closed, and the pressing of the outer peripheral surface of the pre-pipe member comprises reducing a diameter of a portion of the pre-pipe member and forming a reduction portion having a polygonal shape so that the reduction portion has a same number of outer surfaces as a total number of the first inner surfaces and the second inner surfaces.
 2. The method according to claim 1, wherein the polygonal shape is a regular hexagonal shape, the first recess portion has three first inner surfaces including two first side inner surfaces, and a first recessed inner surface that is between the first side inner surfaces, the second recess portion has three second inner surfaces including two second side inner surfaces, and a second recessed inner surface that is between the second side inner surfaces, the arranging of the first die and the second die comprises arranging the first die and the second die such that the first recessed inner surface faces the second recessed inner surface, the pressing of the outer peripheral surface comprises pressing the outer peripheral surface of the pre-pipe member with the three first inner surfaces and the three second inner surfaces, and in the closed state where the first die and the second die are closed, a distance Y between the first recessed inner surface and the second recessed inner surface is from 0.77X to 0.95X where X is an outer diameter of the pre-pipe member.
 3. The method according to claim 1, wherein the pre-pipe member is a shaft of a camshaft to be included in an engine.
 4. The method according to claim 1, further comprising before the pressing of the outer peripheral surface, holding portions of the pre-pipe member with a holding member, the portions of the pre-pipe member being near a portion of the pre-pipe member to be pressed with the first die and the second die.
 5. The method according to claim 4, wherein the holding member has a tubular shape having a through hole therein, and the holding of the portions comprises inserting the pre-pipe member in the through hole.
 6. The method according to claim 1, wherein the polygonal shape is a regular hexagonal shape, the first recess portion has three first inner surfaces including two first side inner surfaces, and a first recessed inner surface that is between the first side inner surfaces, the second recess portion has three second inner surfaces including two second side inner surfaces, and a second recessed inner surface that is between the second side inner surfaces, the arranging of the first die and the second die comprises arranging the first die and the second die such that the first recessed inner surface faces the second recessed inner surface, and the pressing of the outer peripheral surface comprises: pressing the outer peripheral surface of the pre-pipe member with the first side inner surfaces and the second side inner surfaces first and then, according to further pressing of the outer peripheral surface, the first recessed inner surface and the second recessed inner surface being in contact with the outer peripheral surface; and pressing the outer peripheral surface of the pre-pipe member with the first side inner surfaces, the first recessed inner surface, the second side inner surfaces, and the second recessed inner surface in the closed state where the first die and the second die are closed, and forming the reduction portion having a hexagonal cross-sectional shape.
 7. The method according to claim 6, wherein in the closed state, a distance between the first recessed inner surface and the second recessed inner surface is smaller than an outer diameter of the pre-pipe member. 